Disk drive adjusting gain and offset of BEMF velocity sensor during self writing of spiral tracks
A disk drive is disclosed comprising a disk, a head, and a voice coil motor (VCM) operable to actuate the head over the disk, wherein the VCM generates a back electromotive force (BEMF) voltage. At least one reference track is written on the disk, and the head is positioned near a first diameter of the disk. While moving the head from the first diameter toward a second diameter of the disk, the reference track is read and a first estimated state error is measured. While moving the head from the second diameter of the disk toward the first diameter of the disk, the reference track is read and a second estimated state error is measured. A gain and an offset of a velocity sensor are adjusted in response to the first and second estimated state errors.
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When manufacturing a disk drive, concentric servo sectors 20-2N are written to a disk 4 which define a plurality of radially-spaced, concentric servo tracks 6 as shown in the prior art disk format of
In the past, external servo writers have been used to write the concentric servo sectors 20-2N to the disk surface during manufacturing. External servo writers employ extremely accurate head positioning mechanics, such as a laser interferometer, to ensure the concentric servo sectors 20-2N are written at the proper radial location from the outer diameter of the disk to the inner diameter of the disk. However, external servo writers are expensive and require a clean room environment so that a head positioning pin can be inserted into the head disk assembly (HDA) without contaminating the disk. Thus, external servo writers have become an expensive bottleneck in the disk drive manufacturing process.
The prior art has suggested various “self-servo” writing methods wherein the internal electronics of the disk drive are used to write the concentric servo sectors independent of an external servo writer. For example, U.S. Pat. No. 5,668,679 teaches a disk drive which performs a self-servo writing operation by writing a plurality of spiral servo tracks to the disk which are then processed to write the concentric servo sectors along a circular path. Each spiral servo track is written to the disk as a high frequency signal (with missing bits), wherein the position error signal (PES) for tracking is generated relative to time shifts in the detected location of the spiral servo tracks. The read signal is rectified and low pass filtered to generate a triangular envelope signal representing a spiral servo track crossing, wherein the location of the spiral servo track is detected by detecting a peak in the triangular envelope signal relative to a clock synchronized to the rotation of the disk.
The sync marks 24 in the spiral tracks 200-20N may comprise any suitable pattern, and in one embodiment, a pattern that is substantially shorter than the sync mark 10 in the conventional product servo sectors 2 of
In one embodiment, the disk locked clock is further synchronized by generating a timing recovery measurement from the high frequency signal 22 between the sync marks 24 in the spiral tracks 200-20N. Synchronizing the disk locked clock to the high frequency signal 22 helps maintain proper radial alignment (phase coherency) of the Gray coded track addresses in the product servo sectors. The timing recovery measurement may be generated in any suitable manner. In one embodiment, the disk locked clock is used to sample the high frequency signal 22 and the signal sample values are processed to generate the timing recovery measurement. The timing recovery measurement adjusts the phase of the disk locked clock (PLL) so that the high frequency signal 22 is sampled synchronously. In this manner, the sync marks 24 provide a coarse timing recovery measurement and the high frequency signal 22 provides a fine timing recovery measurement for maintaining synchronization of the disk locked clock.
The spiral PES for maintaining the head along a servo track (tracking) while writing the product servo sectors 280-28N may be generated from the spiral tracks 200-20N in any suitable manner. In one embodiment, the PES is generated by detecting the eye pattern in
Once the head is tracking on a servo track, the product servo sectors 280-28N are written to the disk using the disk locked clock. Write circuitry is enabled when the modulo-N counter reaches a predetermined value, wherein the disk locked clock clocks the write circuitry to write the product servo sector 28 to the disk. The spiral tracks 200-20N on the disk are processed in an interleaved manner to account for the product servo sectors 280-28N overwriting a spiral track. For example, when writing the product servo sectors 281 to the disk, spiral track 201 is processed initially to generate the spiral PES tracking error and the disk locked clock timing recovery measurement. When the product servo sectors 281 begin to overwrite spiral track 201, spiral track 200 is processed to generate the spiral PES tracking error and the disk locked clock timing recovery measurement.
In one embodiment, the control circuitry accelerates the head toward the middle diameter of the disk while writing the first part of the bootstrap spiral track as illustrated by the velocity profile shown in
In one embodiment, after launching the head toward the middle diameter of the disk when writing the bootstrap spiral track, the disk will rotate through a known angle before writing the sync mark seam 46, wherein the known angle corresponds to a number of cycles of the disk locked clock. Accordingly, in one embodiment the head is launched when the disk locked clock reaches a first value that is computed relative to a number of cycles before writing the sync mark seam:
where countsPerRev represents the total number of cycles (counts) of the disk locked clock over a full revolution of the disk, spindleZXPerRev represents the number of spindle BEMF zero crossings per revolution of the disk, and the second value represents the disk rotation angle from the launch point until the sync mark seam is written. Launching the head when the disk locked clock reaches the first value computed from the above equation will cause the sync mark seam 46 to be written at an interval that is halfway between two consecutive spindle BEMF zero crossings as illustrated in
In one embodiment, the sync mark seam 46 in the bootstrap spiral track is used to resynchronize the disk locked clock, for example, after a power cycle. Synchronizing the disk locked clock to the sync mark seam 46 essentially initializes the radial and circumferential location of the head to a known state. In addition, after synchronizing the disk locked clock to the sync mark seam 46 the head may be accurately servoed radially over the disk based on the bootstrap spiral track relative to the rotational angle of the disk as determined by the disk locked clock.
Any suitable technique may be employed to detect the sync mark seam 46 in the embodiments of the present invention. For example, the sync mark seam 46 may be detected using first and second correlators matched to the first and second sync marks. The sync mark seam 46 may be detected when there is a switch between the output of the correlators. However, noise in the read signal may reduce the accuracy of the correlators leading to a false detection of the sync mark seam 46.
In one embodiment, the control circuitry calibrates a velocity profile prior to writing the bootstrap spiral track 36 to the disk (
In one embodiment, the interval at step 94 is measured relative to the disk locked clock which represents the rotational phase of the disk. In this embodiment, the target interval corresponds to a target rotational phase of the disk (which may be less or more than one revolution). In one embodiment, the velocity profile is adjusted and the flow diagram of
Any suitable velocity profile may be employed in the embodiments of the present invention.
After calibrating the velocity profile, the bootstrap spiral track 36 is written to the disk using the calibrated velocity profile. In an embodiment shown in
The reference track written at step 100 of
Once the sync mark seam has been located and the modulo-N counter is initialized, the radial location of the head is known relative to the spiral bootstrap track 36. At this point, the control circuitry is able to servo the head to any desired radial location by servoing on the bootstrap spiral track 36 relative to the modulo-N counter as described above. In one embodiment, the control circuitry positions the head near the inner diameter of the disk and writes a circular reference track 112A (
Referring again to
Similar to the inner diameter circular reference track 112A, in one embodiment the outer diameter circular reference track 112B is written at the edge of the constant velocity segment of the velocity profile used to write the spiral tracks. As the head crosses over and reads the circular reference tracks at both the inner and outer diameter, an estimated state error is generated for adjusting the gain and offset of the velocity sensor.
Referring again to
The control circuitry then reverses direction of the head and begins seeking the head toward the inner diameter circular reference track (step 152 of
In one embodiment, the control circuitry writes the bootstrap spiral track 36 having a first substantially constant slope, and writes the gapped spiral tracks having a second substantially constant slope different than the first substantially constant slope. This is illustrated in
In the embodiment of
When seeking the head back to the outer diameter of the disk, the head seeks in the same direction as when writing the bootstrap spiral track. Therefore, in one embodiment there are fewer bootstrap spiral track crossings (and fewer estimated state errors) when seeking the head back to the outer diameter of the disk as compared to the number of bootstrap spiral track crossings when seeking the head toward the inner diameter of the disk while writing a gapped spiral track. This embodiment is illustrated in
In one embodiment, a polarity of the estimated state errors will change depending on the radial seek direction of the head as well as a polarity of the gain error and the offset error. Consider the case where there is zero offset error but a negative gain error (i.e., the gain of the velocity sensor is too high). This will cause the estimated state error to be a first polarity (e.g., positive) when seeking toward the ID of the disk and an opposite polarity (e.g., negative) when seeking toward the OD of the disk. The polarities will reverse if the gain error is positive (i.e., the gain of the velocity sensor is too low). If the offset error of the velocity sensor is non-zero, it will cause a corresponding DC shift in the estimated state errors (positive or negative depending on the polarity of the offset error). Accordingly, in one embodiment a gain error is generated by computing a difference between a first estimated state error generated while seeking in a first direction (e.g., toward the ID) and a second estimated state error generated while seeking in an opposite direction (e.g., toward the OD), and an offset error is generated by computing a sum of the first and second estimated state errors. For example, the first estimated state error may be measured when crossing the ID circular reference track 112A while seeking toward the ID, and the second estimated error may be measured when crossing the OD circular reference track 112B while seeking toward the OD such that:
Gain Error=idStateErr−odStateErr
Offset Error=idStateErr+odStateErr.
In the embodiment wherein an estimated state error is measured at each bootstrap spiral track crossing as well as each circular reference track crossing (
A control error generator 190 generates an error signal 192 representing a difference between an estimated state based on the estimated velocity 170 and a reference value generated by a reference generator 194 (e.g., generated in response to a velocity profile). The error signal 192 is processed by a servo compensator 196 that generates a digital control signal 198 converted 200 to an analog control signal 202 applied to the VCM 33 in order to adjust the velocity of the VCM 33 so as to reduce the error signal 192. A state error generator 204 generates an estimated state error 206 representing a difference between a measured state 208 and an estimated state based on the estimated velocity 170. The measured state 208 is generated at each reference track crossing (circular reference track or bootstrap spiral). The estimated state error 206 is processed by a gain/offset adjustment block 210 as described above in order to adjust the gain of the velocity sensor 168 by adjusting the scalar 184, and to adjust the offset of the velocity sensor 168 by adjusting the offset value 186.
Any suitable control circuitry may be employed to implement the flow diagrams in the embodiments of the present invention, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain steps described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into an SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the steps of the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
Claims
1. A disk drive comprising:
- a disk;
- a head;
- a voice coil motor (VCM) operable to actuate the head over the disk, wherein the VCM generates a back electromotive force (BEMF) voltage; and
- control circuitry operable to: write at least one reference track on the disk; position the head near a first diameter of the disk; while moving the head from the first diameter toward a second diameter of the disk, read the reference track and measure a first estimated state error; while moving the head from the second diameter of the disk toward the first diameter of the disk, read the reference track and measure a second estimated state error; adjust a gain and an offset of a velocity sensor in response to the first and second estimated state errors, wherein the velocity sensor estimates a velocity of the head in response to the BEMF voltage; generate a compensated voltage from the BEMF voltage; and adjust the gain of the velocity sensor by adjusting a scalar for scaling the compensated voltage, wherein the velocity sensor is operable to subtract an offset value from the scaled compensated voltage, and the control circuitry is further operable to adjust the offset of the velocity sensor by adjusting the offset value in response to the first and second estimated state errors.
2. The disk drive as recited in claim 1, wherein the estimated state error comprises an estimated position error.
3. The disk drive as recited in claim 1, wherein the control circuitry is further operable to adjust the gain of the velocity sensor in response to a difference between the first and second estimated state errors.
4. The disk drive as recited in claim 1, wherein the control circuitry is further operable to adjust the offset of the velocity sensor in response to a sum of the first and second estimated state errors.
5. The disk drive as recited in claim 1, wherein the reference track comprises at least one circular reference track.
6. The disk drive as recited in claim 1, wherein the control circuitry is further operable to:
- while moving the head toward the second diameter of the disk, measure a first plurality of estimated state errors;
- sum the first plurality of estimated state errors to generate the first estimated state error;
- while moving the head toward the first diameter of the disk, measure a second plurality of estimated state errors; and
- sum the second plurality of estimated state errors to generate the second estimated state error.
7. The disk drive as recited in claim 6, wherein the reference track comprises at least one bootstrap spiral track.
8. The disk drive as recited in claim 7, wherein the control circuitry is further operable to:
- while moving the head toward the second diameter of the disk, write a gapped spiral track and periodically interrupt the writing to read the bootstrap spiral track to generate one of the first plurality of estimated state errors; and
- while moving the head toward the first diameter of the disk, periodically read the bootstrap spiral track to generate one of the second plurality of estimated state errors.
9. A method of operating a disk drive, the disk drive comprising a disk, a head, and a voice coil motor (VCM) operable to actuate the head over the disk, wherein the VCM generates a back electromotive force (BEMF) voltage, the method comprising:
- writing at least one reference track on the disk;
- positioning the head near a first diameter of the disk;
- while moving the head from the first diameter toward a second diameter of the disk, reading the reference track and measure a first estimated state error;
- while moving the head from the second diameter of the disk toward the first diameter of the disk, reading the reference track and measure a second estimated state error;
- adjusting a gain and an offset of a velocity sensor in response to the first and second estimated state errors, wherein the velocity sensor estimates a velocity of the head in response to the BEMF voltage;
- generating a compensated voltage from the BEMF voltage; and
- adjusting the gain of the velocity sensor by adjusting a scalar for scaling the compensated voltage,
- wherein the velocity sensor is operable to subtract an offset value from the scaled compensated voltage, and the method further comprises adjusting the offset of the velocity sensor by adjusting the offset value in response to the first and second estimated state errors.
10. The method as recited in claim 9, wherein the estimated state error comprises an estimated position error.
11. The method as recited in claim 9, further comprising adjusting the gain of the velocity sensor in response to a difference between the first and second estimated state errors.
12. The method as recited in claim 9, further comprising adjusting the offset of the velocity sensor in response to a sum of the first and second estimated state errors.
13. The method as recited in claim 9, wherein the reference track comprises at least one circular reference track.
14. The method as recited in claim 9, further comprising:
- while moving the head toward the second diameter of the disk, measuring a first plurality of estimated state errors;
- summing the first plurality of estimated state errors to generate the first estimated state error;
- while moving the head toward the first diameter of the disk, measuring a second plurality of estimated state errors; and
- summing the second plurality of estimated state errors to generate the second estimated state error.
15. The method as recited in claim 14, wherein the reference track comprises at least one bootstrap spiral track.
16. The method as recited in claim 15, further comprising:
- while moving the head toward the second diameter of the disk, writing a gapped spiral track and periodically interrupting the writing to read the bootstrap spiral track to generate one of the first plurality of estimated state errors; and
- while moving the head toward the first diameter of the disk, periodically reading the bootstrap spiral track to generate one of the second plurality of estimated state errors.
17. A disk drive comprising:
- a disk;
- a head;
- a voice coil motor (VCM) operable to actuate the head over the disk, wherein the VCM generates a back electromotive force (BEMF) voltage; and
- control circuitry operable to: write at least one reference track on the disk; position the head near a first diameter of the disk; while moving the head from the first diameter toward a second diameter of the disk, read the reference track and measure a first estimated state error; while moving the head from the second diameter of the disk toward the first diameter of the disk, read the reference track and measure a second estimated state error; adjust a gain and an offset of a velocity sensor in response to the first and second estimated state errors, wherein the velocity sensor estimates a velocity of the head in response to the BEMF voltage, while moving the head toward the second diameter of the disk, measure a first plurality of estimated state errors; sum the first plurality of estimated state errors to generate the first estimated state error; while moving the head toward the first diameter of the disk, measure a second plurality of estimated state errors; and sum the second plurality of estimated state errors to generate the second estimated state error, wherein the reference track comprises at least one bootstrap spiral track and the control circuitry is further operable to: while moving the head toward the second diameter of the disk, write a gapped spiral track and periodically interrupt the writing to read the bootstrap spiral track to generate one of the first plurality of estimated state errors; and while moving the head toward the first diameter of the disk, periodically read the bootstrap spiral track to generate one of the second plurality of estimated state errors.
18. A method of operating a disk drive, the disk drive comprising a disk, a head, and a voice coil motor (VCM) operable to actuate the head over the disk, wherein the VCM generates a back electromotive force (BEMF) voltage, the method comprising:
- writing at least one reference track on the disk;
- positioning the head near a first diameter of the disk;
- while moving the head from the first diameter toward a second diameter of the disk, reading the reference track and measure a first estimated state error;
- while moving the head from the second diameter of the disk toward the first diameter of the disk, reading the reference track and measure a second estimated state error;
- adjusting a gain and an offset of a velocity sensor in response to the first and second estimated state errors, wherein the velocity sensor estimates a velocity of the head in response to the BEMF voltage;
- while moving the head toward the second diameter of the disk, measuring a first plurality of estimated state errors;
- summing the first plurality of estimated state errors to generate the first estimated state error;
- while moving the head toward the first diameter of the disk, measuring a second plurality of estimated state errors; and
- summing the second plurality of estimated state errors to generate the second estimated state error,
- wherein the reference track comprises at least one bootstrap spiral track, and the method further comprises:
- while moving the head toward the second diameter of the disk, writing a gapped spiral track and periodically interrupting the writing to read the bootstrap spiral track to generate one of the first plurality of estimated state errors; and
- while moving the head toward the first diameter of the disk, periodically reading the bootstrap spiral track to generate one of the second plurality of estimated state errors.
5455723 | October 3, 1995 | Boutaghou et al. |
5594603 | January 14, 1997 | Mori et al. |
5668679 | September 16, 1997 | Swearingen et al. |
5754352 | May 19, 1998 | Behrens et al. |
5768045 | June 16, 1998 | Patton, III et al. |
5831786 | November 3, 1998 | Boutaghou et al. |
5936788 | August 10, 1999 | Boutaghou et al. |
5982130 | November 9, 1999 | Male |
6005727 | December 21, 1999 | Behrens et al. |
6021012 | February 1, 2000 | Bang |
6025968 | February 15, 2000 | Albrecht |
6091564 | July 18, 2000 | Codilian et al. |
6148240 | November 14, 2000 | Wang et al. |
6191906 | February 20, 2001 | Buch |
6292318 | September 18, 2001 | Hayashi |
6304407 | October 16, 2001 | Baker et al. |
6396652 | May 28, 2002 | Kawachi et al. |
6411453 | June 25, 2002 | Chainer et al. |
6507450 | January 14, 2003 | Elliott |
6512650 | January 28, 2003 | Tanner |
6519107 | February 11, 2003 | Ehrlich et al. |
6563660 | May 13, 2003 | Hirano et al. |
6587293 | July 1, 2003 | Ding et al. |
6690536 | February 10, 2004 | Ryan |
6704156 | March 9, 2004 | Baker et al. |
6731450 | May 4, 2004 | Codilian et al. |
6738205 | May 18, 2004 | Moran et al. |
6795268 | September 21, 2004 | Ryan |
6917486 | July 12, 2005 | Tanner |
6920004 | July 19, 2005 | Codilian et al. |
6924960 | August 2, 2005 | Melkote et al. |
6937420 | August 30, 2005 | McNab et al. |
6943978 | September 13, 2005 | Lee |
6950272 | September 27, 2005 | Rice et al. |
6967799 | November 22, 2005 | Lee |
6977789 | December 20, 2005 | Cloke |
6985316 | January 10, 2006 | Liikanen et al. |
6987636 | January 17, 2006 | Chue et al. |
6989954 | January 24, 2006 | Lee et al. |
6992848 | January 31, 2006 | Agarwal et al. |
7002761 | February 21, 2006 | Sutardja et al. |
7009806 | March 7, 2006 | Zayas et al. |
7019937 | March 28, 2006 | Liikanen et al. |
7042673 | May 9, 2006 | Jeong |
7068463 | June 27, 2006 | Ji et al. |
7072135 | July 4, 2006 | Suzuki |
7082009 | July 25, 2006 | Zayas et al. |
7088533 | August 8, 2006 | Shepherd et al. |
7110207 | September 19, 2006 | Hirano et al. |
7136253 | November 14, 2006 | Liikanen et al. |
7145744 | December 5, 2006 | Clawson et al. |
7193804 | March 20, 2007 | Kheymehdooz |
7196863 | March 27, 2007 | Sakamoto |
7212364 | May 1, 2007 | Lee |
7224546 | May 29, 2007 | Orakcilar et al. |
7230786 | June 12, 2007 | Ray et al. |
7243058 | July 10, 2007 | Du et al. |
7248426 | July 24, 2007 | Weerasooriya et al. |
7256956 | August 14, 2007 | Ehrlich |
7333280 | February 19, 2008 | Lifchits et al. |
7333286 | February 19, 2008 | Jung et al. |
7340968 | March 11, 2008 | Schneider et al. |
7382564 | June 3, 2008 | Everett et al. |
7391583 | June 24, 2008 | Sheh et al. |
7391584 | June 24, 2008 | Sheh et al. |
7405897 | July 29, 2008 | Dougherty et al. |
7411758 | August 12, 2008 | Cheung et al. |
7414809 | August 19, 2008 | Smith et al. |
7421359 | September 2, 2008 | Harmer et al. |
7477471 | January 13, 2009 | Nemshick et al. |
7495857 | February 24, 2009 | Bennett |
7522370 | April 21, 2009 | Sutardja |
7529055 | May 5, 2009 | Laks et al. |
7551387 | June 23, 2009 | Sun et al. |
7561361 | July 14, 2009 | Rutherford |
7619846 | November 17, 2009 | Shepherd et al. |
7623313 | November 24, 2009 | Liikanen et al. |
7639445 | December 29, 2009 | Matsunaga et al. |
7639446 | December 29, 2009 | Mizukoshi et al. |
7656604 | February 2, 2010 | Liang et al. |
7675705 | March 9, 2010 | Mizukoshi et al. |
7688534 | March 30, 2010 | McCornack |
7715143 | May 11, 2010 | Bliss et al. |
7728539 | June 1, 2010 | Smith et al. |
7733588 | June 8, 2010 | Ying |
7737793 | June 15, 2010 | Ying et al. |
7751144 | July 6, 2010 | Sutardja |
7787211 | August 31, 2010 | Kim et al. |
7800857 | September 21, 2010 | Calaway et al. |
7839591 | November 23, 2010 | Weerasooriya et al. |
7852598 | December 14, 2010 | Sutardja |
7876522 | January 25, 2011 | Calaway et al. |
7881004 | February 1, 2011 | Kumbla et al. |
7881005 | February 1, 2011 | Cheung et al. |
20010019463 | September 6, 2001 | Drouin |
20030161065 | August 28, 2003 | Yatsu |
20060171059 | August 3, 2006 | Chan et al. |
20070070538 | March 29, 2007 | Lau et al. |
20070076314 | April 5, 2007 | Rigney |
20070211367 | September 13, 2007 | Lau et al. |
20070291401 | December 20, 2007 | Sun et al. |
20090086357 | April 2, 2009 | Ehrlich |
Type: Grant
Filed: Dec 22, 2011
Date of Patent: Mar 4, 2014
Assignee: Western Digital Technologies, Inc. (Irvine, CA)
Inventors: Brian P. Rigney (Louisville, CO), Edgar D. Sheh (San Jose, CA), Siri S. Weerasooriya (Campbell, CA), Brandon P. Smith (San Jose, CA)
Primary Examiner: Wayne Young
Assistant Examiner: Brian Butcher
Application Number: 13/334,955
International Classification: G11B 5/596 (20060101);